(1) Field of the invention
The present invention generally relates to a resistive sheet thermal transfer printer used in an output device of a computer system, a facsimile machine and so on. The present invention more particularly relates to a resistive sheet thermal transfer printer in which deposit adhered to recording electrodes can be removed.
(2) Description of related art
In a general resistive sheet thermal transfer printer, an ink sheet having a resistance layer, a conductive layer and an ink layer is fed under a condition in which recording electrodes are in contact with the resistance layer of the ink sheet. As a result, deposit of carbon materials forming the resistance layer is accumulated on and around the recording electrodes. Thus, the recording electrodes are worn out by the deposit. If this state is continued, electrical characteristics, representing states in which the recording electrode are in contact with the resistance layer, deteriorate.
To solve the above problem, the following conventional art has been proposed.
Japanese Patent Laid Open Publication 1-216878 discloses a "lapping film cassette".
The lapping film cassette has a lapping film wound around a supplying core and a take-up core. When the supplying core and the take-up core are rotated in a predetermined direction, the lapping film is supplied from the supplying core to the take-up core. The lapping film, the supplying core and the take-up core are housed in a cassette case. The cassette case also houses a mechanism (a cam mechanism) for reciprocating the supplying core and the take-up core in a direction parallel to a direction in which the lapping film is moved.
When a user wishes to abrade the recording electrode, a cassette including the printing ink sheet is replaced with lapping film cassette. The lapping film then is moved, so that the recording electrodes are abraded by the lapping film.
In the above case where the recording electrodes are abraded by the lapping film, the cassette including the printing ink sheet must be replaced with the lapping film cassette. That is, a changing operation of the cassette must be carried out.
Japanese Patent Laid Open Publication 1-225574 discloses a printer in which the recording electrodes can be abraded without changing the cassette including the ink sheet.
In this conventional printer, an ink sheet having a resistance layer, a conductive layer and an ink layer is fed under a condition in which an electrode base and a plurality of recording needles (electrodes) are in contact with the resistance layer of the ink sheet. An image voltage is applied, in accordance with image information, across the electrode base and each of the recording needles. The printer further includes an abrasive mechanism for abrading at least the recording needles, a transferring mechanism for transferring ink from the ink sheet to a recording paper sheet, and a control unit for supplying a control signal, corresponding to the number of recording paper sheets to which ink is transferred, to the abrasive mechanism. The amount of abrasion with which the abrasive mechanism abrades the recording needles is controlled by the control signal. That is, the amount of abrasion of the recording needles is controlled based on the number of recording paper sheets on which images are printed.
Due to an activation of a recording needle (electrode), deposit can be accumulated on and around the recording needle. That is, the amount of ink transferred to the recording paper sheets corresponds to the amount of deposit accumulated on and around the recording needles. However, as the amount of ink transferred to the recording sheet varies in accordance with image data, the total number of recording sheets on which images are printed does not accurately correspond to the amount of deposit accumulated on and around the recording needles (the recording electrodes). Thus, in the above conventional printer, the recording needle can not be effectively abraded.